<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>三角形</title>
  <style>
    .box1, .box2, .box3, .box4 {
      height: 0;
      width: 0;
      float: left;
      border-style: solid;
      margin:10px;
    }
    .box1 {
      border-width: 100px;
      border-color: tomato transparent transparent transparent;
    }
    .box2 {
      border-width: 100px 80px;
      border-color: transparent transparent tomato transparent;
    }
    .box3 {
      border-width: 100px 173px;
      border-color: transparent tomato transparent transparent;
    }
    .box4 {
      border-width: 100px 90px 80px 70px;
      border-color: transparent transparent transparent tomato;
    }
  </style>
</head>
<body>
  <div class="box1"></div>
  <div class="box2"></div>
  <div class="box3"></div>
  <div class="box4"></div>
</body>
</html>